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Build Pictures of My 16" and 24" Homemade Integrating Spheres

For a while now I've been using my calibrated homemade integrating sphere to measure OTF (out the front) lumens of different production lights that were sent to me for review, certain lights that I've modified, and misc. lights that other individuals have sent me for testing purposes.

Lately, however, Ive been thinking that some of you probably often wonder what my sphere looks like. You see my posted OTF lumens data, but some of you probably arent sure what this homemade integrating sphere thing looks like, so I thought Id start this thread for anyone whos interested in looking at more than just my posted measurements .

For me, this quest for the ability to measure actual lumens of different lights all started after reading MrGman's Actual Lumens readings in 6 Lab Sphere IS with SC 5500 control thread, and then BigC's Actual Lumen Readings in 10.5in Sphere thread, which was created when MrGman handed the torch over to BigC.

At that very moment I knew I had to have a sphere of my own for testing different lights, so I contacted BigC to find out more info. BigC pointed me in the right direction and gave me some valuable advice on how to operate the sphere, etc., then I contacted MrGman seeking help in making my sphere as accurate as I could possibly make it (for a homemade sphere).

MrGman graciously, and selflessly guided me through the entire build and calibration process of not one sphere, but two spheres. The first sphere we built together was my 16 sphere. It worked great, and still works great; thats the sphere that I use most often for testing. But I later found out that I needed to either cut a larger opening in my 16 sphere, which would reduce accuracy, or build a larger sphere to measure these larger lights that were heading my way for testing.

I opted to build the larger sphere because it would give me improved accuracy over creating a larger source port in my 16 sphere, higher lumen measuring capacity, plus I really didnt want to cut on the finely tuned 16 sphere that MrGman and myself spent so much time building and calibrating .

Thus, my 24 sphere was born . Of course this was after BigC upgraded to a 24 sphere for higher lumen capacity after he pegged his meter testing one of the high powered SST-90 Maglite builds.

If you're wondering what my spheres were calibrated with, I used multiple lights that MrGman tested in the real Lab Integrating Sphere that he had access to at his work. This still doesn't qualify my sphere as being equal to the real $10,000 sphere, but it's much more accurate than simply using lights that are the same type of light that such and such manufacturer or such and such member measured in their sphere that made X amount of lumens, which means this one should be close.

Yeah it would be in the ballpark by simply assuming one light makes the same amount of light as another, but that's not good enough for me (yes I readily admit that I'm a perfectionist ). If all I wanted to do was compare relative brightness of different lights it would be perfectly fine to use this sphere without calibrating it to exact, known lumen output sources. This would work well at showing which lights are brighter than others, whether the light holds its output well for 20 minutes or drops like a rock in less than 3 minutes, but my goal is to provide OTF lumen measurements that are as close to the real deal as I can get with what I have to work with.

All of my testing is done in a completely dark room with no ambient lighting in the room at all, not even an alarm clock , so none of my measurements are skewed from ambient lighting. My meter also has a photopic response curve feature, which offers improved accuracy when taking measurements of lights that have different wavelengths. .

Now it's time for some pictures.

These pictures are a mix of 16 and 24 build pictures. The process is pretty much the same:

First I cut the port for the light source in each sphere:

Then I cut the sensor port for my meter, then test fit:

Next I installed a baffle and tested to make certain no direct light will hit the sensor:

My meter:

A piece of paper is cut to fit the exact OD of every light that I test. This greatly reduces the amount of light lost around the bezel of lights that are smaller than the source port. This is the same method MrGman and BigC used during testing.:

Re: Build Pictures of My 16" and 24" Homemade Integrating Sphere's

Hey ti-force. I guess this is one of the threads that got zapped! I just finished a sphere that is more or less identical to this one, got the AEMC meter as well.

Two questions.

First, what is your calibration number? I've talked with bigchelis and will eventually get around to calibrating with his lights/sphere, but in the mean time I'd like to get some rough figures out of mine.

Second, if I put in a light with an MCE and flood reflector I get something like 38K lux. If I use an identical light...but with an aspheric...I get something like 18k lux. It seems like this is one of the limitations of the home made sphere...any idea how to get better readings with the aspheric? To me it seems like the interior is not reflective enough and the small hot spot must be allowing a lot of the light to "get lost." Does that make any sense?

Re: Build Pictures of My 16" and 24" Homemade Integrating Sphere's

Hey ti-force. I guess this is one of the threads that got zapped! I just finished a sphere that is more or less identical to this one, got the AEMC meter as well.

Two questions.

First, what is your calibration number? I've talked with bigchelis and will eventually get around to calibrating with his lights/sphere, but in the mean time I'd like to get some rough figures out of mine.

Second, if I put in a light with an MCE and flood reflector I get something like 38K lux. If I use an identical light...but with an aspheric...I get something like 18k lux. It seems like this is one of the limitations of the home made sphere...any idea how to get better readings with the aspheric? To me it seems like the interior is not reflective enough and the small hot spot must be allowing a lot of the light to "get lost." Does that make any sense?

Re: Build Pictures of My 16" and 24" Homemade Integrating Sphere's

Originally Posted by archer6817j

... Second, if I put in a light with an MCE and flood reflector I get something like 38K lux. If I use an identical light...but with an aspheric...I get something like 18k lux. It seems like this is one of the limitations of the home made sphere...any idea how to get better readings with the aspheric? To me it seems like the interior is not reflective enough and the small hot spot must be allowing a lot of the light to "get lost." Does that make any sense?

Thanks!

As previously stated aspheric lenses are highly inefficient. If you are using an add on aspheric on top of a light that already has a reflector in the back, most of these do not properly collect all the light off of the reflector and send it down the middle of the lens. The lens itself typically loses light off of each surface if its not fully anti reflective (AR coated). most are not. At the very least you lose 8% of your light right there due to internal reflections. The lack of reflectivity of styrofoam for the very tight beam of an aspheric flashlight beam is a minor issue compared to the losses at the flash light itself. White Styrofoam is highly reflective compared to a lot of other materials.

You should send pictures and/or provide info of your sphere system and your light and the aspheric lens, how it mounts, do you take the reflector out or not. Things like that would be useful. The tighter the beam the harder it is to calibrate to a home made IS without having a known output value of the light with the aspherical lens on it from a calibrated professional sphere system.

I can take some photos soon but in the mean time...I built a sphere basically identical to the one in the thread. The light head is machined by me, no reflector, aspheric is the front element, no glass.

What I'm hearing is that it might be impossible to get a good reading in this sphere without getting a calibration off a real sphere with this exact light.

So, maybe lumens is a poor way to rate an aspheric light? Would lux at "x" distance be a better way to compare aspheric lights?

Given the above, will I have the same problem accurately measuring lights that have throwy reflectors (small hot spots)?

Re: Build Pictures of My 16" and 24" Homemade Integrating Spheres

That's the 24" I got; however, I think you might be fine with the 16" . I actually found that the larger sphere tends to "under read" for the lights I have that are 500+ lumens. What I did find that worked really well was to put an acrylic globe inside the styrofoam sphere, kind of russian doll style. Then the meter port looks at the side of the acrylic globe as opposed to the opposite wall of the sphere. I've actually made three different spheres and the "combo" sphere seems to be the most accurate...as far as I can tell. All three read extremely close at say 300 lumens or less, but the pure foam spheres seem to read too low at high lumens. I talked to someone else about this and the theory is that the large number of lumens overwhelm the foams ability to diffuse the light and you effectively "loose" some. The double sphere diffuses twice an (the theory is) traps more of the actual lumens. I think the globe I orders was a 14" from lightsnglobes on ebay. This fits inside the 16" foam sphere with about an inch of space all the way around. I spaced it off the bottom with some square "air pack" from crate and barrel. I also ordered the "necked" version so the neck practically touches in inside of the foam sphere.

Re: Build Pictures of My 16" and 24" Homemade Integrating Spheres

Sorry, I have been away for a while (sort-of lost interest in the flashlight hobby and gained interest in another hobby), but yes, Plasteel is where I purchased my sphere's from also.

Archer,

Have you tried using a fine grit sandpaper and sanding the sheen off of the interior of the sphere? I've found this to be a great, simple, and cost effective solution to better light diffusion. In fact, Saabluster tested this method against a coating that he used in his sphere and found it to be nearly as effective diffusing the light as the coating (the difference was minute, if I remember correctly). I would post a link to the thread, but a quick search didn't find it. Just be sure to use a find sandpaper if you try this method. Also, and as you know, the light capacity changes with size of the sphere, but I think a lot of the differences in measurement (or at least in my case) is actually because of the way my meter tracks. The larger sphere has higher light capacity, so meter reading is lower and of course a smaller sphere produces a higher number. And since I divide this number by the measured lumens of my reference lights, I arrive at my divide by constant for all other lights. But of course, I'm no pro, and I'm no genius, either, so..... At any rate, the difference in lumen measurement between my 18" sphere and my 24" is minute. And of course another variable that comes into play from one sphere to another is the distance at which the sensor is from the inside plane of the sphere. It should be as close as possible to the inside plane of the sphere without actually breaking through the inside plane. Best of luck with your sphere's; I'm sure they will work well for you.